The Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) is an evolving high speed, high capacity standard for a User Equipment (UE) emerging as a globally accepted standard. The LTE that is being deployed globally operates in Packet Switched (PS) domain. Currently, UEs equipped with LTE technology utilize LTE PS domain to handle data traffic while voice traffic is handled by legacy Circuit Switched (CS) networks (legacy Radio Access Technologies (RATs)) such as Global System for Mobile communications (GSM), Universal Mobile Terrestrial System (UMTS) and GSM EDGE Radio Access Network (GERAN). To support CS domain communication such as voice calls the UE in LTE has to switch to CS supporting legacy RATs.
The Circuit Switched Fallback (CSFB) procedure standardized by 3GPP technical specification enables the UE to perform this switching during Mobile Originated (MO) or Mobile Terminated Call (MT). The 3GPP standard defines Inter-RAT (I-RAT) for mobility (switching) between LTE and earlier 3GPP technologies such as UMTS and GERAN and vice versa. To acquire a legacy RAT during I-RAT switching the 3GPP standard provides procedures like redirection, reselection, and hand over and so on.
In accordance with existing 3GPP standard for redirection based CSFB procedure, when the CS call is attempted while UE is in LTE, then the UE starts an Extended Service Request (ESR) procedure. When the ESR is received by E-UTRAN Node B (eNB) of the LTE network, the eNB provides the UE with Radio Resource Control (RRC) connection release along with redirection request including the target RAT frequency on to which the UE can camp for CS call. Further, after the completion of CS call, it is important for the network operators to move the UE to the EUTRAN for providing higher data rates and better user experience to its subscribers.
In the existing system, the network (can be either UTRAN or GERAN) may command the UE to redirect or handover to EUTRAN from UTRAN after the completion of CSFB call on the current RAT. However, not all the networks are following this approach, as it requires some changes in the network side. Though the CS call is ended in the UTRAN, the UE maintains the PS data session with the UTRAN. In such scenario, it is important to move the UE to idle mode for reselection to EUTRAN.
When the UE is in mobility across different radio access networks, there is a possibility that the UE loses the coverage of the EUTRAN. The UE connects to the UTRAN for obtaining the packet data services when it loses the coverage of the EUTRAN. Further, during the mobility, the UE may detect the EUTRAN and it is important to move the UE to the EUTRAN upon its detection for providing enhanced packet data services to the UE.
In the light of above discussion, it is desirable to have a mechanism that allows the UE to reselect or redirect to the EUTRAN upon completion of CS call on UTRAN/GERAN for providing enhanced packet data services. It is further desirable to have a mechanism for bringing the UE to idle mode for reselection or redirection to the LTE network.